> Except that Ember is one of the heaviest front-end frameworks in terms of file size.

IIRC react requires nearly 300MB worth of npm packages just to get the hello world example to run. How does Ember fare in comparison?

It changed a lot and you don't have to use all the feature if you don't need it. React with data support, router, etc can be super big... and latest Ember without Ember Data and tree shaking is small, so you win a lot of developer time and money and you end up with a well maintainable code, which can be understand by others in the first day, because of conventions over configurations. ;) IMHO Ember.js is still the best option for frontend, especially if you build a serious Web Application.